Which is Better? A Budget with “Challenge” or a Budget with “Reserve”?

In the defense contracting world budgeting is typically done under a rigorous “earned value management system” (EVMS) that usually includes keeping aside 10% of the budget for use as a “management reserve”.  This can then be doled out in bits and pieces as needed to fund changes in what needs to be done (“scope” in the project-organized world) and solutions for problems that arise during the course of business.  It also allows people within the organization to cope with unexpected changes without feeling like they are endangering the project or organization when they have to ask for more funding.  They all still have to do what they can to stay within budget, but it gives the appearance that upper management accepts that unexpected changes happen and are going to be reasonable in helping people dealing with them.  That’s not how budgets are typically presented in the rest of the business world, however.